a) Field of the Invention
The present invention relates to musical tone signal generating techniques, and more particularly to techniques of generating musical tone signals by using a plurality of tone generators (sound sources) of different types.
b) Description of the Related Art
Various tone generators of different types are known, including pulse code modulation (PCM) tone generators, frequency modulation (FM) tone generators, and physical model tone generators. Each tone generator generates musical tone waveforms in a different manner to achieve particular tone colors. For example, the physical model tone generator is suitable for generating tone colors of stringed instruments and wind instruments.
A player can play both melody and accompaniment parts by using an electronic musical instrument. In general, tone colors of melody and accompaniment parts are often changed during performance. For example, tone colors of a stringed instrument are assigned to melody parts, whereas tone colors of a keyboard instrument are assigned to accompaniment parts. In an ideal, typical example, musical tone signals for melody parts are generated by using a physical model tone generator rich in musical expression, and musical tone signals for accompaniment parts are generated by using a PCM or FM tone generator capable of generating a number of musical tones relatively inexpensively.
As above, each tone generator generates some tone colors excellently but some tone colors poorly. If a tone generator superior to generating musical tones of a particular tone color is selectively used, it is possible to make musical performance with fine melody sounds of a musical piece or with substantial accompaniment sounds. In order to realize such performance with conventional techniques, a plurality of tone generators of different types are interconnected via musical instrument digital interface (MIDI) to configure an integrated tone generator system mixed with a plurality of tone generators. However, in this case, the physical scale of the system becomes bulky and the system becomes expensive.
Each tone generator has a common part more or less although its configuration changes from one type to another. If a plurality of tone generators are used, the same common part is used in duplicate by each tone generator so that the system becomes inefficient and expensive.